How to troubleshoot Mercedes Benz Air Conditioner System, Read Sensor Data, Reset Unit
Entering Diagnostic Trouble Code (DTC) Display Mode
1) Turn ignition on. Press down arrow push button until “LO” is shown in A/C-heater control panel temperature display window.
2) Within 20 seconds, simultaneously press REST and defrost push buttons for more than 2 seconds. The Light Emitting Diode (LED) in the recirculated air push button will blink and the display window will show “di R”.3) Press AUTO push button repeatedly, recording each DTC,until all DTCs are displayed. Permanent malfunctions are displayed first. See DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION tables.
4) If no permanent malfunctions are stored, the display window shows “En d”. Press AUTO push button again. Intermittent DTCs will be displayed. Intermittent malfunctions are recognizable by the degree (°) symbol displayed along with the DTC (example: “04 °”).
5) If no intermittent malfunctions are stored, the display window shows “En° d”. Proceed to ERASING DIAGNOSTIC TROUBLE CODES.
Erasing Diagnostic Trouble Codes
1) After display window shows “En° d”, press AUTO push button once again. Display window should show “dE L” (delete).
2) To erase DTCs, simultaneously press down and up arrow push buttons for more than 5 seconds. The display window should show “- –“. If not erasing DTCs, press the AUTO push button. The permanent DTCs will again be displayed. Proceed to EXITING DTC DISPLAY MODE.
Exiting DTC Display Mode
Simultaneously press down and up arrow push buttons until the pre-selected temperature setting of “72 °F” is displayed. Turn ignition off.
DCT error codes list:
B1226 – In-car temperature sensor (B10/4)
B1227 – Outside temperature indicator temperature sensor (B14)
B1228 – Heater core temperature (B10/1)
B1229 – Heater core temperature (B10/1)
B1230 – Evaporator temperature sensor (B10/6)
B1231 – ECT sensor (B11/4)
B1232 – Refrigerant pressure sensor (B12)
B1233 – Refrigerant temperature sensor (B12/1)
B1234 – Sun sensor (B32)
B1235 – Emissions sensor (B31)
B1241 – Refrigerant fill
B1416 – Coolant circulation pump (M13)
B1417 – Duovalve (Y21y1), left
B1418 – Duovalve (Y21y2), right
B1419 – Electromagnetic clutch (A9k1)
B1420 – Idle speed increase
B1421 – Pulse module (N65)
B1422 – Series interface (K1) connection to instrument cluster (A1)
B1423 – Switchover valve block (Y11)
B1424 – Activated charcoal filter actuator (A32m2) open
B1425 – Activated charcoal filter actuator (A32m2) closed
B1432 – Non-USA DTC
B1459 – Series interface (K2) connection to instrument cluster (A1)
B1462 – Wide open throttle (WOT) position signal: diesel engines
Climate control as a diagnostic tool
READING SENSOR VALUES
1) Turn ignition on. Simultaneously press down and up arrow push buttons until the pre-selected temperature setting of “72 °F” is displayed. Press the AUTO push button.
2) Press REST push button for more than 6 seconds. The display window will alternately show “01” and an in-car temperature of “72 °F”, or “LO” if there is an open circuit, or “HI” if there is a short circuit.
3) By pressing the windshield air distribution push button, the next ascending test step is displayed. By pressing the footwell air distribution push button, the next descending test step is displayed. See SENSOR VALUE DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION table. Press REST push button to exit reading sensor values mode.
01 = In-car temp sensor
02 = outside temp sensor
03 = left heat exchanger (heater core) temp sensor
04 = right heat exchanger sensor
05 = evaporator sensor
06 = coolant temp
07 = refrig. pressure in bar
08 = refrig temp sensor (23*9 = 23.9deg C)
09 = nothing
10 = Blower control voltage (great for evaluating blower controller problems)
11 = emissions sensor (B31) e.g. 3.1 = 31.v
12 = sun sensor 4.2 = 4.2v
20 = aux fan control 6.1 = 6.1ma (max 10ma)
21 = engine speed
22 = vehicle speed
23 = Circuit 58d e.g. 99 = 99% of battery voltage
24 = BATTERY VOLTAGE e.g. 12.5 = 12.5v
30 = left rear air conditioning heat exchanger temp sensor (not all vehicles; obviously)
31 = right side
32 = rear evap temp sensor
33 = blower control voltage rear 0.8(MIN) – 6.0(MAX)
34 = left rear temp selector
35 = right side
38 = software status e.g. 37 rear air conditioning
38 = hardware status e.g. 37 , rear air conditioning
40 = control module version software status (?)
41 = control module version menu hardware status
42 = control module variant code 1st number
43 = variant code second number.